There is interest in the use of trench capacitors for use as the storage node in the memory cells of dynamic random access memories (DRAMs). Such capacitors offer the potential of relatively large capacitances with the consumption of relatively little surface area, which permits a higher density of memory cells in a silicon chip of a given size. Typically such vertical cells have been filled with doped polysilicon because of its convenience of use.
However, as the cross section of the vertical trench has been shrunk while its depth has been increased to get a desired capacitance with smaller consumption of chip surface area, the resulting increased resistance has become a matter of concern, since it increases the time to charge/discharge the capacitor, thereby limiting performance. While it has been recognized that the substitution of a material, such as a metal, for the doped polysilicon fill, would result in a lower resistance, it has proven difficult to find a suitable metal for filling trenches with aspect ratios much in excess of 10. The present invention is addressed to this problem.